TagHelper for <meta> tags

I'm trying to use TagHelpers to rewrite some of the meta tags in my website.

For each meta tag that has the following attributes: data-data-main,data-src, I would like to replace the value of one of those attributes.

For example, this is the original:

<meta name="js" content="script" data-async="true" data-data-main="requirejs/product-overview/init" data-src="/js/libs/require.js">

I want to transform this into this:

<meta name="js" content="script" data-async="true" data-data-main="http://cdn.website.nl/8c87f33ca5acc7fdb9186d6a497642784685aabade058d3530bdf6d30168cfcd.js" data-src="/js/libs/require.js">

The only thing that changed is the data-data-main attribute: it now points to an URL on the CDN instead of a local file.

I made a custom TagHelper to help me achieve this goal:

[HtmlTargetElement("meta", Attributes = "[data-data-main],[data-src]")]
public class MetaScriptTagHelper : TagHelper
{
    private readonly BluenotionSiteSettings _bnSiteSettings;
    private readonly SiteTemplateService _templateService;

    public MetaScriptTagHelper(BluenotionSiteSettingsFiller bnSiteSettingsFiller, SiteTemplateService templateService)
    {
        _bnSiteSettings = bnSiteSettingsFiller.Create(HttpContext);
        _templateService = templateService;
    }

    [ViewContext]
    public ViewContext ViewContext { get; set; }

    private HttpContext HttpContext => ViewContext.HttpContext;

    public override void Process(
        TagHelperContext context, TagHelperOutput output)
    {
        var dataDataMainValue = context.AllAttributes["data-data-main"].Value.ToString();
        var localPath = @".\wwwroot\js\" + dataDataMainValue.Replace('/', '\\') + ".js";
        var siteTemplateId = _templateService.SiteTemplateBySiteIdAsync(_bnSiteSettings.SiteId);
        var cdnPath = _templateService.GetResourceByName(siteTemplateId, localPath);
        output.Attributes.Add("data-data-main", cdnPath);
    }
}

Sadly, it returns an exception:

Found a malformed 'meta' tag helper. Tag helpers must have a start and end tag or be self closing.

(no further stacktrace/information to indicate what the malformed meta tag was)

I can't debug what the malformed meta tag is so I have no idea where the problem lies. Any suggestions?

Solution

Okay, I feel really stupid for not checking this before I posted the question, but apparantly, it was the input that was messing the TagHelper up.

It says Tag helpers must have a start and end tag or be self closing. Apparantly, this means that the meta element that comes in must have a end tag or be self closing, which (as shown in my before/after samples) my meta elements did not have.

So to fix, I simply had to make the input meta tags self closing (i.e. add a / before the closing >):

<meta name="js" content="script" data-async="true" data-data-main="requirejs/product-overview/init" data-src="/js/libs/require.js"/>`